Pyrotechnic charge structure

ABSTRACT

A pyrotechnic charge structure, in particular for use as propellant in a rocket motor, is disclosed. The charge structure has a predetermined longitudinal extension and cross sectional area adapted to the intended purpose. The pyrotechnic charge structure ( 1; 2; 3; 4 ) is in cross sectional view in cellular form aimed at having similar wall thickness for all the cells of the charge structure. The wall ( 6 ) of the cells comprises the pyrotechnic charge, i.e. the propellant, and each cavity of the cells occupies air or oxygen-rich gas.

[0001] The present invention relates to a pyrotechnic charge structure, in particular for use as propellant in a rocket motor, which charge structure has a predetermined longitudinal extension and transversal cross sectional area adapted to the intended purpose.

[0002] In some types of weapons for various uses, it is particularly important that the propellant for a projectile is burnt extremely fast, e.i. within 5-10 milliseconds. Typical examples are shoulder launched weapons like M-72, Carl Gustav, or weapons where the marksman is standing adjacent to the weapon. Such weapons are not allowed to have extensive tail-off, i.e. that they need to burn out instantly without prolonged burning time with to that decreasing gas pressure. In shoulder fired weapons the projectile is shot out from a launcher. Here it will be of most importance that the propellant is burnt out before the projectile leaves the launcher. If not, the combustion gases, and possibly flashes and residual products from the combustion will be thrown toward the face and body of the marksman and cause severe injuries.

[0003] According to the present invention is a pyrotechnic charge structure of the introductorily described type provided, which is distinguished in that the pyrotechnic charge structure, in transversal cross section, is in cellular form aimed at having similar wall thickness for all the cells in the charge structure, and in which the wall of the cells comprises the pyrotechnic charge, i.e. the propellant, and each cavity of the cells occupies air or oxygen-rich gas.

[0004] The advantage with this pyrotechnic charge structure is as follows. Subsequent to the ignition of the propellant it will be burning from all of the surfaces simultaneously and perpendicular to the surfaces of the cell walls, or webs, until it all is simultaneously burnt out. This may happen extremely fast since the thickness of the cell walls is at a minimum at the same time as the said thickness is substantially the same all around the cell. In addition is a high burning pressure generated (rapidly up and rapidly down). Such a propellant is a high-energy fuel that can be utilised in an effective way for launching missiles/rockets.

[0005] In a preferable embodiment the cells are in form of a polygonal structure. In one for the time being particularly preferred embodiment, the cells have form of a honeycomb structure. Other conceivable embodiments of the cell structure are a lattice structure, for example having square cellular form, a triangle structure, a circle structure and an oval structure.

[0006] Advantageously the charge can be a fuel of the composite type, like HTPB (Hydroxyl Terminated Polybutadiene), HTPE (Hydroxyl Terminated Polyether), CTPB (Carboxyl Terminated Polybutadiene), or moulded double base or other mouldable powder-/propellant types and combinations.

[0007] According to size of the weapon, the wall thickness of the cells will be adapted to the actual dimensions, and the wall thickness of the cells will typically be in order of magnitude 1-5 mm.

[0008] Other and further objects, features and advantages will appear from the following description of for the time being preferred embodiments of the invention, which are given for the purpose of description, without thereby being limiting, and given in context with the appended drawings where:

[0009]FIG. 1 shows a cross sectional view through a motor casing for a rocket motor having a first embodiment of the pyrotechnic charge structure according to the invention,

[0010]FIG. 2 is analogous to that shown in FIG. 1 of a second embodiment of the pyrotechnic charge structure according to the invention,

[0011]FIG. 3 is analogous to that shown in FIG. 1 of a third embodiment of the pyrotechnic charge structure according to the invention,

[0012]FIG. 4 is analogous to that shown in FIG. 1 of a fourth embodiment of the pyrotechnic charge structure according to the invention, and

[0013]FIG. 5 shows a typical pressure/time graph for a pyrotechnic charge structure according to the invention.

[0014] Reference is firstly given to FIG. 1 that shows a motor casing 10, which per se could be manufactured of any suitable material, such as steel, aluminium, titanium or a composite. The latter material is increasingly more current, and in particular this consists of an epoxy/polyester reinforced with carbon fibres, aramid fibres or glass fibres.

[0015] Internally of the motor casing 10 is a layer 9, or a liner, of insulating material provided. The insulating material can be rubber (EPDM), phenolic paper, phenolic silica etc.

[0016] Further, internally of the layer 9 is an inert filler material 8 provided. The filler material 8 stabilises and retains a centrally located pyrotechnic charge, constituting a propellant, in the motor casing 10. The pyrotechnic charge has a predetermined longitudinal extension within the motor casing 10 and this extension together with the transversal cross sectional area will be adapted to the field of use and the purpose of the weapon. Without being limiting, the longitudinal extension can typically be from close to zero to 50 cm as example. In transversal cross section the charge has the appearance of a cellular structure 1 having aimed at similar wall thickness for each individual cell of the charge. The cell walls, termed the webs 6, constitute the propellant proper and the cavities of the cells are filled with air or oxygen-rich gas. Indicated web thickness will be in order of magnitude 1-5 mm. The embodiment shown in FIG. 1 is in form of a polygon structure, in particular a honeycomb structure.

[0017] Without being a limitation, a manner how to manufacture the propellant will be to mould a mixture of the composite type, for example HTPB (Hydroxyl Terminated Polybutadiene), HTPE (Hydroxyl Terminated Polyether), CTPB (Carboxyl Terminated Polybutadiene), mouldable double base powder/fuel.

[0018] The propellant can be ignited from the front as well as rear, by a pyrotechnic primer (not shown), such as a pyromesh igniter or charge made of black powder or BKNO3 in an igniter housing of plastic/metal (pyrogenic primer), or bag fixed to the internal surface just ahead of or just behind the charge, etc. In this case it will probably be best to use a pyromesh igniter and mounted ahead of the propellant. After being ignited, the fuel will burn simultaneous from all of the surfaces in the cells and perpendicular to the web surfaces of the cells until all the fuel is simultaneously burnt out. As illustrated on the figure, those cell webs 6 that burn from both sides have double thickness compared to those abutting the inert filler material 8. It is to be understood that in order to obtain the aimed at rapid combustion, in addition to achieve optimum effect, certain relations between the surface area of the cell webs 6, the thickness of the web 6 and the volume of air or oxygen present in the cellular structure 1 will apply.

[0019] The cell structure may per se adopt any suitable form that provide the conditions presented above in addition to substantially constant web thickness of the cells for the entire charge. FIG. 2 shows a second embodiment of the cellular structure in form of a lattice structure 2. Here squarely designed cells are illustrated. Other variants can be rhombus form, rectangular form etc.

[0020]FIG. 3 shows a third embodiment of the cellular structure in which each cell has trilateral form that together constitute a triangular structure 3.

[0021] In FIG. 4 each individual cell has circular form. This fourth embodiment of the cell construction comprises a circular structure 4. Another alternative will be cells in form of ovals.

[0022] A substantial advantage with mouldable composite fuel/powder is that it is not too temperature dependent. I.e. that the energy in the fuel during launching either the ambient temperature is cold, normal or hot provides approximately the same power. When the temperature independence is little, the hit likelihood is getting far better for a rocket/missile. This condition has to do with the normal scattering of a weapon. A certain scattering is difficult to avoid, but by use of a temperature independent fuel one factor that contributes to scattering will be eliminated.

[0023] The ballistic properties are improved with mouldable composite charges having thin webs in the cells. By such a cellular design the charge will burn out extremely fast, a few milliseconds, and by a nearly “square” pressure/time graph. This is illustrated in closer detail in FIG. 5. The vertical axis shows the pressure course and the horizontal axis illustrates the time lapse. By the firing of a charge the pressure will instantly rise very abrupt up to a level, be maintained at this level during combustion and in turn descend abrupt down to zero subsequent to completed combustion. The integral of this graph is an expression for the total impulse generated by the propellant.

[0024] The pure mechanical strength properties of the illustrated charge structures, and the rigidity thereof, are substantially improved. Mechanical strength is an important property in view of those forces that act in a weapon of this type, such as acceleration, vibration, chock, change of temperature, coldness and hotness. 

1. A pyrotechnic, moulded charge structure, in particular for use as propellant in a rocket motor, in which the charge structure has a predetermined longitudinal extension and transversal cross sectional area adapted to the intended purpose, characterised in that the pyrotechnic, moulded charge structure (1;2;3;4), in transversal cross section, is in cellular form aimed at having similar wall thickness for all the cells of the charge structure, and the walls (6) of the cells comprises the pyrotechnic charge, i.e. the propellant, and each cavity of the cells occupies air or oxygen-rich gas.
 2. A pyrotechnic, moulded charge structure according to claim 1, characterised in that the cells are in form of a polygonal structure.
 3. A pyrotechnic, moulded charge structure according to claim 1, characterised in that the cells are in form of a honeycomb structure (1).
 4. A pyrotechnic, moulded charge structure according to claim 2, characterised in that the cells are in form of a lattice structure (2).
 5. A pyrotechnic, moulded charge structure according to claim 2, characterised in that the cells are in form of a triangular structure (3).
 6. A pyrotechnic, moulded charge structure according to claim 1, characterised in that the cells are in form of a circular structure (4).
 7. A pyrotechnic, moulded charge structure according to claim 1, characterised in that the cells are in form of an oval structure.
 8. A pyrotechnic, moulded charge structure according to any of the claims 1-7, characterised in that the charge is a fuel of the composite type, such as HTPB, HTPE, CTPB, moulded double base powder/fuel.
 9. A pyrotechnic, moulded charge structure according to any of the claims 1-8, characterised in that the charge has a longitudinal extension of 1-50 cm.
 10. A pyrotechnic, moulded charge structure according to any of the claims 1-9, characterised in that the cell walls (6) have a web thickness in the order of magnitude 1-5 mm. 